updated macos settings in cmakelists

CMakeLists.txt

@@ -45,14 +45,17 @@ message(STATUS "ITK_DIR=${ITK_DIR} pybind11_DIR=${pybind11_DIR}")
 # --------------------------------------------------
 #             build settings
 # --------------------------------------------------
-# set -DAPPLE_ARM64=ON on cmake command line for arm64 build
+# set -DAPPLE=ON and -DAPPLE_ARM64=ON on cmake command line for arm64 build
 # when building with freesurfer, CMAKE_C_COMPILER and CMAKE_CXX_COMPILER will be specified on the cmake command line
-if("${APPLE_ARM64} STREQUAL "ON")
-  set(CMAKE_OSX_ARCHITECTURES "arm64")
-  add_definitions(-DARM64 -DDarwin -DPNG_ARM_NEON_OPT=0)
-else()
-  set(CMAKE_OSX_ARCHITECTURES "x86_64")
+if(${APPLE})
+  if("${APPLE_ARM64} STREQUAL "ON")
+    set(CMAKE_OSX_ARCHITECTURES "arm64")
+    add_definitions(-DARM64 -DDarwin -DPNG_ARM_NEON_OPT=0)
+  else()
+    set(CMAKE_OSX_ARCHITECTURES "x86_64")
+  endif()
 endif()
+
 message(STATUS "CMAKE_C_COMPILER=${CMAKE_C_COMPILER}, CMAKE_C_COMPILER_ID=${CMAKE_C_COMPILER_ID}, CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}, CMAKE_CXX_COMPILER_ID=${CMAKE_CXX_COMPILER_ID}")
 
 # warnings